COS 105-6
The facultative symbiont Rickettsia protects an invasive whitefly against entomopathogenic Pseudomonas syringae strain
Facultative endosymbionts can benefit insect hosts in specific contexts, such as by protecting hosts against pathogens. It may be difficult to know how facultative symbionts are benefiting hosts in some populations, especially in the case of protection from cryptic pathogens. The sweet potato whitefly (Bemisia tabaci), an invasive agricultural pest, can possess facultative endosymbionts of the genus Rickettsia. Rickettsia is common in some whitefly populations where it improves host fitness in ways that are not entirely known. We investigated the interaction of a recently discovered cryptic pathogen of hemipteran insects, the common epiphytic bacterium Pseudomonas syringae, with whiteflies and Rickettsia. To determine if Rickettsia can protect whiteflies against cryptic pathogens, we tested whitefly lines with identical nuclear genetic backgrounds, but differing in Rickettsia infection status, for mortality after oral exposure to the pathogen.
Results/Conclusions
Sweet potato whiteflies became infected with P. syringae in either in vitro feeding assays or by feeding on plants painted with the bacteria. The bacteria multiplied in the insects and caused very high mortality (80-90%) within four days. The presence of Rickettsia provided whiteflies some protection against the pathogen, slowing the rate of death. The impact of Rickettsia was most pronounced at low infection levels from on plant exposure. Little is known about how insects and most environmental bacteria, including P. syringae, interact. Pseudomonas syringae is a common plant pathogen and is widely found on plant surfaces so it could have significant impacts on whitefly populations. These results also suggest that Rickettsia may benefit hosts by protecting against cryptic pathogens, which could contribute to the prevalence of Rickettsia in some populations. These findings may be useful in the biological control of whiteflies.